The present invention relates to the formation of freeze-dried cakes or plugs of stable structure by using glycylglycine as a freeze-drying cake-former or bulking agent. The invention further relates to a stabilised freeze-dried composition comprising proteins and glycylglycine.
Proteins are relatively unstable in the aqueous state and undergo chemical and physical degradation resulting in a loss of biological activity during processing and storage. Lyophilisation or freeze-drying is a well-established method for preserving proteins for storage.
A lyophilisation cycle is usually composed of three steps: freezing, primary drying and secondary drying. In the freezing step, the protein solution is cooled until it is adequately frozen. Bulk water in the protein solution forms ice at this stage. This ice sublimes in the primary drying stage, which is conducted by reducing chamber pressure below the vapour pressure of the ice using a vacuum. Finally, sorber or bound water is removed at the secondary drying stage under reduced chamber pressure and elevated shelf temperature. The process produces a material known as a lyophilised cake. Prior to use the cake is reconstituted. The standard practice is to add back a volume of pure water.
In order to preserve protein conformation, activity and stability, the protein solution prone to be lyophilised usually contains agents facilitating this, so-called lyoprotectants and cryoprotectants. Cryoprotectants are agents which provide stability to the protein from freezing-induced stresses; however, the term also includes agents that provide stability, e.g. to bulk drug formulations during storage from non-freezing-induced stresses. Lyoprotectants are agents that provide stability to the protein during water removal from the system during the drying process, presumably by maintaining the proper conformation of the protein through hydrogen bonding. Cryoprotectants can also have lyoprotectant effects.
When water removal has taken place, the protein and agents are in the form of a dried xe2x80x9ccakexe2x80x9d. This cake needs to have good properties as to form and structure, i.e. it must not collapse, as such collapsed cakes are hard or even impossible to dissolve (reconstitute) before use. One or more so-called bulking agents are added to the solution before lyophilisation. Bulking agents are agents which provide good lyophilised cake properties and which help the protein overcome various stresses associated with the lyophilisation process (for example shear/freezing). Bulking agents also help to form an pharmaceutically elegant product and help to maintain protein activity levels during the freeze-drying process and subsequent storage. Examples of frequently used bulking agents include mannitol, glycine, sucrose, lactose, etc. The agents also contribute to the tonicity of the formulations.
Therapeutic proteins for injection or infusion are often formulated and stored as lyophilised products. The lyophilised samples may be kept in long-term storage and reconstituted at a later time by adding a suitable administration diluent just prior to patient use.
High concentrations of salt in a sample will normally make the removal of water time consuming and difficult and it will be difficult to obtain a suitable freeze-dried cake.
There is still a need in the art for providing methods for improving freeze-drying processes and products, such as providing bulking agents that improve the properties of freeze-dried cakes or plugs.
It has now been found that glycylglycine can be used as a bulking agent in freeze-drying, giving structural stability to the freeze-dried plug or cake, and at the same time act as a stabiliser primarily against aggregation of proteins. Furthermore, by combining the functions as buffer substance (in solution before lyophilisation) and as bulking agent in one compound, the number of excipients in the freeze-dried formulation is reduced.
Glycylglycine can be used alone or in combinations with sugars, e.g. sucrose, and/or in combination with sugar alcohols, e.g. mannitol, and/or in combination with cyclodextrins, and/or amino acids, such as glycine or arginine. It has also been found that glycylglycine may advantageously be used as a freeze-drying cake-former when used in freeze-dried formulations containing high concentrations of salts ( greater than 5 mg/ml of salts).
Flandrois, C. et al., Annales de Biologie Clinique, Vol 47, pp. 252-260 (1989) relates to the use of glycylglycine as a buffer substance.
Davis, G. J. et al., Archives Biochem.Biophys., Vol.311, pp. 307-312 (1994) relates to the use of glycylglycine as a diagnostic reagent in the study of specific enzymatic reactions.
European Patent No. EP 359 201 B relates to the use of glycylglycine or glycylglycylglycine as a stabiliser of blood or plasma.